Radio receiving apparatus



March 8, 1938 L. E. THOMPSON RADIO RECEIVING APPARATUS Filed April 2, 1934 INVENTOR Lerlz'e E. Thom 0m BY 621W HIS ATT ORNEY Patented Mar. 8, 1938 UNITED SATES PATENT OFFlCE RADIO RECEIVING APPARATUS Application April 2, 1934, Serial No. 718,624 in Great Britain April 8, 1933 11 Claims.

This invention relates to automatic volume control for radio-receiving apparatus and has for its object to provide improved arrangements for effecting control of this character.

Automatic control of the volume of reproduction of sound in radio-receiving apparatus is usually effected by varying the grid potential in relation to the cathode potential of one or more of the valves of the apparatus, in accordance with the strength or amplitude of the carrier wave received in such a manner as to render this grid potential increasingly less positive or more negative as the strength of the received carrier wave increases and thus correspondingly to reduce the degree of amplification effected by the valve which is thus controlled.

In order to prevent the undesired reduction in the amplification of received signals of low strength the automatic volume control is preferably arranged to become effectively operative only at and above a predetermined signal strength, this action being termed delayed automatic volume control, while in order further to prevent undesired received signals of low strength from being reproduced the amplification is re duced to an extremely low value for all signals of below a minimum strength, thus effecting what is termed quiet automatic volume control. The grid bias potential required for controlling the amplification of the volume controlled valve is preferably derived from a resistance arranged to be traversed by a current which is due to the resultant of two opposed potentials, one of which is proportional to the strength of the received carrier wave, the other potential being derived from a suitable source of direct current and adjusted to a predetermined value by means of a potentiometer for instance. The circuit of the resistance includes a unidirectional current carrying device such as a dry surface contact rectifier, with the result that the current traversing the resistance undergoes a very considerable change in magnitude when its direction is reversed due to one of these potentials becoming higher than the other as the strength of the received signal increases or decreases, thus giving the delayed volume control action above re ferred to.

According to the principal feature of the invention the automatic volume control is arranged to be effected by the combined action of a normal control arrangement of the kind above described and a negative or oppositely acting arrangement of a similar kind with the result that as the strength or amplitude of a received signal in,-

creases, as the tuning of the receiving apparatus approaches that for the desired wave-length, the amplification of this signal is gradually increased to a maximum and subsequently, as the tuning eventually attains that for the desired wavelength, is controlled in the normal manner. In other words the amplification is caused to be relatively very low for low signal strengths, then rises to a maximum for a predetermined signal strength and is again, reduced for higher signal strengths, thus preventing the reproduction of undesired very weak signals and the undue weakening of somewhat stronger signals.

In carrying the invention into practice, the improved volume control may be effected by providing two opposite controlling potentials each due to a circuit containing a dry surface contact rectifier and supplied with current due to the resultant of a potential proportional to the strength of the received carrier wave and a constant potential, the two circuitsbeing so arranged that one of the controlling potentials in-- creases and the other decreases as the strength of the carrier wave increases.

The invention is illustrated by way of example in the accompanying drawing, Figure 1 of which is a diagrammatic View of the circuit connections of a portion of a radioreceivin-g apparatus embodying one form of the invention,

Figure 2 is a curve diagram illustrating the ac tion of the apparatus,

Figure 3 being a view similar to Figure 1 illustrating the invention. as applied to a battery operated receiving apparatus.

Referring now first to Figure 1, it will be seen that the coupling transformer between the last H. F. stage and the detector of the apparatus is indicated at T comprising a primary winding 1 and two secondary windings 2, 3. The circuit of the secondary winding 2 includes a dry surface contact rectifier D1 constituting the detector of the apparatus connected in series with a resistance R1, a point 4 intermediate the detector D1 and the resistance R1 being connected to the input circuit of the first. L. F. stage of the apparatus by means of a conductor 5.

The point 4 is also connected through a dry surface contact rectifier V1 in its reversed current direction to a conductor 6 and a resistance 1 to a control grid 8 of a valve 9 which may be either an 1-1. F. or L. F. amplifying valve having variablemu characteristics and serving as a volume control valve.

The cathode l6 of'the valve 9 is connected through a conductor II to a point B in a potentiometer resistance I2 one terminal of which is connected to an earth conductor I3 and the other to the negative H. T. terminal of the apparatus as shown. The conductor 6 leading from the rectifier V1 is connected to the point B in the resistance I2 through a volume control resistance R2. The resistance 12 is arranged to be traversed by a considerable current due for example to the operation of the valves of the apparatus with the result that the point B is at a negative potential relative to the potential of the earthen conductor I3.

The circuit of the secondary winding 3 of the transformer T includes a dry surface contact rectifier V2 connected in series with a resistance R3 and the point 54 between the rectifier V2 and the resistance R3 is connected through a rectifier V3 in its reverse current direction to the point I5 between the conductor 5 and the resistance R2. The opposite end I6 of the resistance R3 is connected through a resistance R; to a point A in the potentiometer resistance I2 which is negative relative to the point B above referred to.

The operation of the apparatus is as follows:

The potential at which the cathode til of the valve 9 is maintained during operation is evidently the potential of the point B of the resistance I2 and is somewhat negative relative to earth. The potential of the grid 8 of the valve 9 is the potential of the point I5 which will vary in accordance with the strength of the signal being received, due to the action of the transformer windings 2, 3 and their associated circuits.

Considering first the action of the transformer winding 2, so long as a signal is not being re ceived by the apparatus the resistance R1 will not be traversed by current derived from the winding 2. A small current will, however, traverse the resistance R1 from the earth conductor i3, through resistance R1, rectifier V1 in its reverse current direction, resistance R2 to the point B in the resistance I2. Owing to the large drop of potential in the rectifier V1, the point I5 will be substantially at the potential of the point B so that potential of the grid 8 of the valve 9 will be slightly positive relative to the cathode I!) by an amount corresponding to the drop of potential in the resistance R2. As the received signal strength increases a direct current potential due to the current traversing the transformer winding 2 and the detector D1 will be maintained at the terminals of the resistance R1 and will cause an increase in the current and drop of potential across the resistance R1 thereby reducing the current in the resistance R2 and the positive potential of the point I5 and consequently of the grid 8.

As soon as the potential developed at the terminals of the resistance R1 by the received signal current is equal to the potential between the conductor I3 and the point B in the resistance I2, the flow of current in the resistance R2 will be reduced to zero and the potential of the point l5 and the grid 8 will be the same as that of the cathode Iii.

A further increase in the received signal strength will cause the potential developed across the resistance R1 by the current traversing the detector D1 to be greater than the potential between the conductor I3 and the point B, whereupon current will be caused to flow through the resistance R2 and the rectifier V1 in the reverse current direction of this rectifier. The potential of the point I5 will, under these conditions, undergo a sudden and rapid change due to the reversal of the direction of the flow of current in the rectifier V1 and the point I5 and the grid 8 will become increasingly negative relative to the cathode II).

The action above described is illustrated by curve M of Figure 2 in which the horizontal line OK represents the potential of the cathode Ill of the valve 9 and the vertical line POP represents the positive or negative potential of the grid 8 for no signal being received. The vertical and horizontal ordinates of the curve M represent the potential of the grid and the strength of the received signal respectively and it will be seen that the potential of the grid 8 has a small positive value when a signal is not being received, this potential gradually falling to zero as the signal strength increases and then rapidly falling to a relatively large negative value.

Considering now the action of the transformer winding 3; when a signal is not being received current flows from the point B in the potentiometer resistance I2 through resistance R2, rectifier V3 in its normal current direction, resistance R3 and resistance R4 to the point A in the resistance l2. Owing to the potential drop in the resistance R2, the point I5 will be maintained at a relatively large negative potential under these conditions as indicated in curve N of Figure 2.

When a signal is received the current supplied from the transformer winding 3 will develop a potential at the terminals of the resistance R3 opposing the potential at these terminals due to the action of the potentiometer resistance I2 above described and the current traversing the resistance R2 will be reduced as the signal strength increases, thereby causing the potential of the point I5 to become less negative until at a predetermined signal strength when the potential impressed on the resistance R3 due to the Winding 3 exceeds the potential thereon due to the resistance I2, the direction of the flow of current in the resistance R2 will be reversed so that this current then traverses the rectifier V3 in its reverse current direction. As a result the potential of the point I5 will rapidly become decreasingly negative as the signal strength further increases as indicated by the form of the curve N of Figure 2.

The actual potential of the point I5 for various values of received signal strength will evidently be the resultant of the actions of the transformer windings 2 and 3 above described, that is to say will be the sum of the potentials indicated by the curves M and N of Figure 2. This resultant potential of the point I5 and consequently of the grid 8 of the valve 9 is represented by the curve S of Figure 2 which is the sum of the curves M and N and it will thus be evident that for weak signals received the potential of the grid 8 will be negative thereby efiecting a corresponding reduction in amplification of the valve 9 and ensuring the desired quiet action. As the received signal strength increases the potential of the grid 8 becomes less negative and eventually at a predetermined signal strength attains a maximum positive value corresponding to the normal maximum amplification. A further increase in signal strength beyond this value causes the potential of the grid 8 to become less positive and eventually to become rapidly increasingly negative so as to effect thedesired reduction in the amplification of the ,porary reduction in signal strength due to fading for instance shall not cause the suppression of the signal and this may be effected by suitablys adjusting the time constant of the quiet volume control circuit as for instance by the provision of a suitable condenser C1 connected as shown in Figure l.

, Referring now to Figure 3, the invention is illustrated as applied to a simpler form of receiving apparatus in which the various potentials required are arranged to be obtained from primary or secondary batteries.

In this form of apparatus the cathode H! of the control valve 9 is connected directly to the earth conductor 13, the resistance R1 being connected at one end to the conductor leading to the first L. F. stage of the apparatus and at the other end to the negative terminal of a battery H, the positive terminal of which is connected to the earth conductor l3.

The circuit supplied from the transformer winding 3 including the rectifier V2 and the resistance R3 also includes a battery it opposing the action of the winding 3 as regards the flow of current in the resistance R3, one end of this resistance being connected to the earth conductor I3 through a battery l9 as illustrated.

From the explanation given above it will be evident that the potential of the point l5 to which the grid 8 of the valve 9 is connected will vary in accordance with the strength of the received signal so as to effect the desired quiet delayed volume control.

Itwill be understood that the invention is not limited to the particular circuit connections or arrangements of the elements of the volume control apparatus above described and illustrated by way of example, which may be varied in many respects without exceeding the scope of the invention.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. Radio receiving apparatus provided with arrangements for effecting automatic volume.

control of the kind described, in which this control is effected by impressing upon the volume controlled valve a grid bias potential which results from two opposed currents flowing in a circuit containing a resistance and a unidirectional current carrying device, one of said currents being derived from a radio frequency valve of the apparatus and having a magnitude which is substantially inversely proportional to the strength of the received carrier wave, and the other of said two currents being derived from a source of substantially constant potential connected with said circuit, means for adjusting said other current such that when no signal is received by the apparatus said grid bias potential will have a relatively large negative value which rapidly changes to a slowly increasing positive value under theinfluence of a decrease in said one current resulting from an increase in signal strength.

2. In combination with radio receiving apparatus of the kind described, a volume control valve, a circuit including a unidirectional current carrying device and a resistance, means for passing a first current through said circuit which is substantially inversely proportional to the strength of the received carrier wave for causing a potential drop in said resistance, means for passing a second current of substantially constant Value irrespective of signal strength through said resistance in a direction such as to oppose said first current for causing an opposing potential drop in said resistance, and means for impressing the combined potential drop resulting from the flow of said two currents in said resistance upon the grid of said volume control valve for controlling the volume of the output of said apparatus.

3. In combination with radio receiving apparatus of the kind described, a volume control valve, a first circuit including a first unidirectional current carrying device and a resistance, a second circuit including a second unidirectional current carrying device and said resistance, means for establishing in said first circuit a first current which is substantially directly proportional to the strength of the received carrier wave, means for establishing in said second circuit a second current which is substantially inversely proportional to the strength of the received carrier wave, means for passing a third current of substantially constant value irrespective of signal strength through said resistance in a direction such as to oppose said first and second currents for causing an opposing potential drop in said resistance, and means for impressing the combined potential drop resulting from the flow of said three currents in said resistance upon the grid of said volume control valve for controlling the volume of the output of said apparatus.

4. In combination with radio receiving apparatus of the kind described, a volume control valve, a circuit including a dry surface contact rectifier and a resistance, means for passing a first current substantially inversely proportional to the strength of the received carrier wave through said circuit, means for passing a second current of substantially constant value irrespective of signal strength in the opposite direction through said circuit so that at a predetermined strength of the carrier Wave said two currents will substantially neutralize whereby the efiective resistance of said rectifier will change abruptly to cause an abrupt change in the magnitude of said first current for rendering the control function of said first current more effectual, and means for controlling said volume control valve by the com bined potential drop resulting from the flow of said two currents in said resistance to thereby control the volume of the output of saidapparatus.

5. In combination with radio receiving apparatus of the kind described, a volume control valve, a circuit including a unidirectional current carrying device and a resistance, means for passing a first current substantially inversely proportional to the strength of the received carrier wave through said first circuit, means for passing a second current of substantially constant value irrespective of signal strength through said circuit in a direction such as to oppose the flow of said first current, means for impressing the combined potential drop resulting from the flow of said two currents in said resistance upon the grid of said volume control valve for controlling the volume of the output of said apparatus, and means for adjusting the level of said second current to thereby adjust the signal strength at which said volume control valve becomes efiective.

6. In radio receiving apparatus of the kind described, the method of providing automatic volume control, which comprises passing three currents in a circuit containing .a unidirectional current carrying device, the first and second of said currents being substantially directly and inversely proportional respectively to the strength of the received carrier wave, and the third of said currents being substantially constant irrespective of signal strength, and which comprises applying the resultant drop in at least a portion of said circuit traversed by said three currents to the grid of a volume control valve to control the volume of the output of said apparatus.

'7. In combination with radio receiving apparatus, a volume control valve, a first circuit including a first unidirectional current carrying device and a resistance, a second circuit including a second unidirectional current carrying device and said resistance, means for establishing in said first circuit a first current which varies in accordance with a given function of the magnitude of the received carrier wave, means for establishing in said second circuit a second current which varies in accordance with a difierent function of the magnitude of said carrier wave, means for passing a third current of substantially constant value irrespective of signal strength through said resistance in a direction such as to oppose said first and second currents, and means for impressing the combined potential drop resulting from the flow of said three currents in said resistance upon the grid of said volume control valve for controlling the volume of the output of said apparatus.

8. In combination with radio receiving apparatus, a volume control valve, a detector circuit for said apparatus including a dry surface contact detector, a second circuit including a unidirectional current carrying device and a resistance, means for energizing said second circuit from the output potential of said detector circuit to cause a current to flow in a given direction through said resistance, a third circuit including a unidirectional current carrying device, means for establishing a unidirectional potential in said third circuit which varies as a function of the magnitude of the received carrier Wave, a fourth circuit including a unidirectional current carrying device and said resistance, means for energizing said fourth circuit from the unidirectional potential established in said third circuit to cause a current to fiow in said given direction through said resistance, means for passing a substantially constant current irrespective of signal strength in the opposite direction through said resistance, and means for impressing the combined potential drop resulting from the flow of said three currents in said resistance upon the grid of said volume control valve for controlling the volume of the output of said apparatus.

9. In combination with radio receiving apparatus of the kind described, a volume control valve, a circuit including a unidirectional current carrying device and a resistance, means for impressing the potential drop in said resistance upon the grid of said volume control valve, means for passing a first current substantially proportional to the strength of the received carrier wave through said circuit in a direction such that said first current when alone traversing said resistance causes a. positive grid bias potential to be impressed upon the grid of said valve, and means for passing a second current of substantially constant value irrespective of signal strength through said resistance in a direction opposite to that of said first current, whereby the combined potential drop due to the flow of said two currents in said resistance is effective in controlling the grid bias of said volume control valve to thereby control the volume of the output of said apparatus.

10. In combination with radio receiving apparatus oi the kind described, a volume control valve, a circuit including a resistor having a nonlinear resistance-voltage characteristic, means for impressing the potential drop in at least a portion of said circuit upon the grid of said valve, means for passing a first current substantially proportional to the strength of the received carrier wave through said circuit in a direction such that said first current when acting alone causes a positive grid bias potential to be impressed upon the grid of said valve, and means for passing a second current of substantially constant value irrespective of signal strength through said portion of the circuit in a direction opposite to that of said first current, whereby the combined potential drop due to the flow of said two currents in said circuit portion is efi'ective in controlling the grid bias of said volume control valve to thereby control the volume of the output of said apparatus.

11. In combination with radio receiving apparatus of the kind described, a volume control valve, a circuit, means for impressing the potential drop in at least a portion of said circuit upon the grid of said valve, means for passing a first current substantially proportional to the strength of the received carrier wave through said circuit in a direction such that said first current when acting alone causes a positive grid bias potential to be impressed upon the grid of said valve, and means for passing a second current of substantially constant value irrespective of signal strength through said portion of the circuit in a direction opposite to that of said first current, whereby the combined potential drop due to the flow of said two currents in said circuit portion is effective in controlling the grid bias of said volume control valve to thereby control the volume of the output of said apparatus.

LESLIE ERNEST THOMPSON. 

